Ultralight Bivy Sack Guide

Ultralight Bivy Sack Guide

Ultralight bivy sacks are used by backpackers using floorless shelters to protect their sleeping bags or quilts from moisture and their heads from biting insects, as a kind of substitute for the inner tent that you find in more conventional double wall tent setups. They’re basically sleeping bag covers with a waterproof floor that have mosquito netting over the face.

Most ultralight bivy sacks have just enough room inside for a sleeping pad and a sleeping bag or sleeping quilt, but sleeping in them really isn’t as claustrophobic as it might look and there’s still plenty of room to sleep on your side or prop your head up on your arm to read at night.

Ultralight Bivy Sack under a floorless pyramid trap
Ultralight Bivy Sack under a floorless pyramid trap

Many ultralight bivy sacks have a cord loop that you can tie to the underside of your shelter to hold the bug netting up off of your face when you sleep. You can also tie this cord to the rafters in a trail shelter and use your bivy to protect you from bugs and mice. Your bivy sack also provides a wee bit more privacy inside a shelter if you want to change your clothes.

Ultralight Bivy Sack in use inside an Appalachian Trail Shelter
Ultralight Bivy Sack in use inside an Appalachian Trail Shelter

When sleeping under a tarp, a bivy sack helps protect your sleep system from splash-back, which occurs when rain bounces off the ground and under your tarp and on your sleeping gear. This can be an issue if you have a narrow rectangular tarp, but is less of a concern if you use a wide or shaped tarp, whose sides are tied close to the ground in bad weather.

Most ultralight bivy sacks don’t impart much extra warmth to your sleeping bag or quilt at night, although they will block a breeze from chilling you. They are often made with a top fabric that is quite breathable to help vent any condensation build-up at night. The top fabric is so light weight that you can sleep on top of your sleeping bag or quilt and use like a sheet in very hot weather to keep the bugs from biting your legs and arms.

Ultralight Bivy Sack under a floorless Cuben Fiber Tarp
Ultralight Bivy Sack under a floorless Cuben Fiber Tarp

Ultralight bivy sacks are quite delicate pieces of gear made by hand and must be treated gently if you want them to last. If you buy a bivy sack that has a zipper, it’s good to lubricate it periodically with McNet’s Zip Tech so it doesn’t snag, and to dry your bivy sack out after every trip you take to avoid mildew. If you see black mildew spots begin to form on the bivy fabric, washing your bivy sack out with diluted Mirazyme will eliminate it and prevent damage to the fabric.

Other Types of Bivy Sacks

Most of the bivy sacks that you’ll find at REI or other outdoor retailers are heavier than the hand-made ultralight bivy sacks that can buy from smaller gear manufacturers. While many of these are intended primarily for winter use in a snow cave or shelter, some have bug netting over the face and can also be used in warmer weather such as the REI Superlight Bivy Sack or Outdoor Research Interstellar Bivy.

Some bivy sacks are so bombproof that they can even be classified as tents including the Outdoor Research Alpine Bivy Sack and the NEMO GoGo Elite 1 Bivy Sack. 

Unlike Ultralight Bivy sacks, none of these other bivy types are intended to be used with floorless shelters, but are meant to be standalone shelters in their own right. It is confusing that they’re all called bivy sacks, so I hope this post has helped clarify the differences between them.

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  1. Can you tell me where to purchase a setup like Ultralight Bivy Sack under a floorless pyramid trap? Would this work in the high sierras, late summer early fall?


    • Click on the links (blue type) in the article above to go to the sellers of the bivvs mentioned. I suggest you also look at Mountain Laurel Designs.

  2. hello, i am planning a shelter setup with ddsuperlight tarp,thermarestzlitesol,and the north face bluekazoo , with 30l backpack should i use a bivy sack ? it is necesssery ? if i am not use bivy sack what can happen ? greetings from turkey .

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